text: /*
   * Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   *
   * 1. Redistributions of source code must retain the above copyright notice, this
   *    list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #pragma once
  
  #include <AK/Function.h>
  #include <AK/NonnullRefPtr.h>
  #include <AK/Optional.h>
  #include <AK/Queue.h>
  #include <LibCore/CEventLoop.h>
  #include <LibCore/CObject.h>
  #include <LibThread/Lock.h>
  #include <LibThread/Thread.h>
  
  namespace LibThread {
  
  template<typename Result>
  class BackgroundAction;
  
  class BackgroundActionBase {
      template<typename Result>
      friend class BackgroundAction;
  
  private:
      BackgroundActionBase() {}
  
      static Lockable<Queue<Function<void()>>>& all_actions();
      static Thread& background_thread();
  };
  
  template<typename Result>
  class BackgroundAction final : public Core::Object
      , private BackgroundActionBase {
      C_OBJECT(BackgroundAction);
  
  public:
      static NonnullRefPtr<BackgroundAction<Result>> create(
          Function<Result()> action,
          Function<void(Result)> on_complete = nullptr)
      {
          return adopt(*new BackgroundAction(move(action), move(on_complete)));
      }
  
      virtual ~BackgroundAction() {}
  
  private:
      BackgroundAction(Function<Result()> action, Function<void(Result)> on_complete)
          : Core::Object(&background_thread())
          , m_action(move(action))
          , m_on_complete(move(on_complete))
      {
          LOCKER(all_actions().lock());
  
          this->ref();
          all_actions().resource().enqueue([this] {
              m_result = m_action();
              if (m_on_complete) {
                  Core::EventLoop::main().post_event(*this, make<Core::DeferredInvocationEvent>([this](auto&) {
                      m_on_complete(m_result.release_value());
                      this->unref();
                  }));
                  Core::EventLoop::main().wake();
              } else
                  this->unref();
          });
      }
  
      Function<Result()> m_action;
      Function<void(Result)> m_on_complete;
      Optional<Result> m_result;
  };
  
  }
  